Magnetic field sensors and sensng circuits

ABSTRACT

A magnetic sensor for sensing an external magnetic field includes first and second electrodes and first and second magnetic tunneling junctions. The first and second electrodes are disposed over a substrate; and the first and second magnetic tunneling junctions are conductively disposed between the first and second electrodes and connected in parallel between the first and second electrodes. The first and second magnetic tunneling junctions are arranged along a first easy axis of the magnetic sensor. The first magnetic tunneling junction includes a first pinned magnetization and a first free magnetization, and the second magnetic tunneling junction includes a second pinned magnetization and a second free magnetization. The first free magnetization and the second free magnetization are arranged substantially in parallel to the first easy axis and in substantially opposite directions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. application Ser. No.13/097,083, filed on Apr. 29, 2011, which claims the benefit of priorityto U.S. Provisional Application No. 61/383,734, filed on Sep. 17, 2010.These applications are hereby incorporated by reference in theirentities.

TECHNICAL FIELD

The disclosure relates to a magnetic field sensing apparatus and, moreparticularly, to three-axis magnetic field sensors.

BACKGROUND

Electronic compasses are integrated in various electronic products toimprove navigational performance or other functionalities of thoseproducts. For example, an electronic compass can be used in connectionwith a global positioning system (GPS) to improve position sensing. Atraveling direction sensed by the GPS reflects movements of an objectcarrying the GPS. However, when the object stops or travels at a lowspeed, conventional GPS often cannot determine the orientation andposition of the object. An electronic compass can provide information ofa geomagnetic field, thereby improving the position sensing by the GPS.

Hall devices and magneto-resistive devices can usually provide sensingof an external magnetic field. Magneto-resistive devices, includinganisotropic magneto-resistor (AMR), giant magneto-resistor (GMR), andtunneling magneto-resistor (TMR), may provide better sensitivity thanHall devices.

Existing magneto-resistive devices may have significant limitationsdepending on the devices or their configurations, designs, orapplications. For example, AMR magnetic field sensors are generallylimited to two-axis sensing. GMR magnetic field sensors can only operatein a unipolar mode, because they can detect only the magnitude of thesensed magnetic field but not the exact direction of the field. Inaddition, it may be difficult to achieve a multi-axis integratedmagnetic field sensor using conventional GMR, TMR, or AMR.

SUMMARY

In some embodiments, a magnetic sensor for sensing an external magneticfield is provided. The magnetic sensor comprises: a first electrode anda second electrode disposed over a substrate; a first magnetic tunnelingjunction and a second magnetic tunneling junction conductively disposedbetween the first electrode and the second electrode and connected inparallel between the first electrode and the second electrodes. Thefirst magnetic tunneling junction and the second magnetic tunnelingjunction are arranged along a first easy axis of the magnetic sensor.The first magnetic tunneling junction includes a first pinned layerhaving a first pinned magnetization, a first free layer having a firstfree magnetization, and a first tunneling layer between the first pinnedlayer and the first free layer. The second magnetic tunneling junctionincludes a second pinned layer having a second pinned magnetization, asecond free layer having a second free magnetization, and a secondtunneling layer between the second pinned layer and the second freelayer. The first free magnetization and the second free magnetizationare arranged substantially in parallel to the first easy axis and insubstantially opposite directions. The first pinned magnetization andthe second pinned magnetization each form an angle of about 45 or 135degrees with the first easy axis.

In other embodiments, a circuit for sensing an external magnetic fieldis provided. The circuit comprises: a first voltage source for providinga source voltage; a first magnetic sensor for providing a referencecurrent; a second magnetic sensor for sensing an external magneticfield, a conductivity of the second magnetic sensor varying in responseto the external magnetic field; a bias voltage unit connected to thefirst magnetic sensor and the second magnetic sensor for providing abias voltage to the first magnetic sensor and the second magneticsensor; a clamp voltage current mirror unit for generating the referencecurrent of the first magnetic sensor and mirroring the current to thesecond magnetic sensor; and a signal transfer amplifying unit forgenerating an output voltage and an additional current to compensate thechanges in the conductivity of the second magnetic sensor.

In still other embodiments, a method for forming a magnetic sensor isdisclosed. The method comprises: disposing a first magnetic tunnelingjunction and a second magnetic tunneling junction between a firstelectrode and a second electrode on a substrate. The first magnetictunneling junction and the second magnetic tunneling junction arealigned along a first easy axis. The first magnetic tunneling junctionincludes a first pinned layer and a first free layer, and the secondmagnetic tunneling junction includes a second pinned layer and a secondfree layer. The method further comprises connecting the first magnetictunneling junction and the second magnetic tunneling junction inparallel between the first electrode and the second electrode; setting afirst pinned magnetization in the first pinned layer of the firstmagnetic tunneling junction and a second pinned magnetization in thesecond pinned layer of the second magnetic tunneling junction along afirst pinned direction by subjecting the magnetic sensor to one or moreexternal magnetic fields during an annealing process; and generateampere fields on the first free layer of the first magnetic tunnelingjunction and the second free magnetization in the second free layer ofthe second magnetic tunneling junction by a setting current. The firstand second pinned magnetizations each form an angle of about 45 or 135degrees with the first easy axis. The first and second freemagnetizations are parallel to the first easy axis and in substantiallyopposite directions.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings provide further understandings of thedisclosed embodiments. The drawings illustrate the disclosed embodimentsand, together with the description, serve to explain the disclosedembodiments.

FIGS. 1A and 1B illustrate a cross-sectional view and a top view of amutual supplement tunneling magneto-resistor (MS-TMR), respectively,consistent with disclosed embodiments.

FIG. 2A illustrates another top view of the MS-TMR of FIGS. 1A and 1B.

FIG. 2B illustrates curves representing theoretical conductivities ofthe MS-TMR of FIGS. 1A and 1B.

FIG. 3A illustrates a top view of another MS-TMR.

FIG. 3B illustrates curves representing simulated conductivities of theMS-TMR of FIG. 3A.

FIG. 4 illustrates a two-axis magnetic field sensor formed on asubstrate, consistent with disclosed embodiments.

FIG. 5A illustrates a top view of a Z-axis magnetic field sensor,consistent with disclosed embodiments.

FIGS. 5B and 5C illustrate cross-sectional views of the Z-axis magneticfield sensor of FIG. 5A, consistent with disclosed embodiments.

FIGS. 6A and 6B illustrate a coordinate transformation for the inclinedsurface of the substrate of the Z-axis magnetic field sensor of FIG. 5A,consistent with disclosed embodiments.

FIG. 7 illustrates a top view of a Z-axis magnetic field sensor,consistent with disclosed embodiments.

FIG. 8 illustrates a top view of a three-axis magnetic field sensor,consistent with disclosed embodiments.

FIG. 9 illustrates an annealing process for setting the pinnedmagnetizations of the MS-TMR of FIG. 8, consistent with disclosedembodiments.

FIG. 10 illustrates a circuit diagram for sensing an external magneticfield, consistent with disclosed embodiments.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments, examplesof which are illustrated in the accompanying drawings. The followingdescription refers to the accompanying drawings in which the samenumbers in different drawings may represent the same or similarelements. The implementations set forth in the following descriptions ofexemplary embodiments do not represent all implementations consistentwith the disclose embodiments. Instead, they are merely examples ofsystems and methods consistent with aspects related to the discloseembodiments.

Magnetic sensors comprising one or more mutual supplement tunnelingmagneto-resistors (MS-TMRs) are provided for sensing an externalmagnetic field. Methods are also provided for sensing the externalmagnetic field by using the magnetic sensor. Magnetic sensors disclosedherein may produce a substantially or approximately linear output inresponse to the external magnetic field. In some embodiments, magneticsensors may be integrated in electronic circuits for generatingelectronic signals in response to an external magnetic field.

FIG. 1A illustrates a cross-sectional view of a magnetic sensor 10including a MS-TMR 100, and FIG. 1B shows a top view of the magneticsensor 10, consistent with disclosed embodiments. As shown in FIG. 1A,the MS-TMR 100 has a multi-layer structure, including a bottom electrode102 made of a conductive material, such as Ta, Ti, TiN, TaN, Al, Cu, Ru,etc., and formed on a substrate 90; a top electrode 106 made of asimilar conductive material; and a first and a second Magnetic TunnelingJunction (MTJ) devices 110 a and 110 b formed between the bottomelectrode 102 and the top electrode 106. As such, the first MTJ device110 a and the second MTJ device 110 b are connected in parallel betweenthe top electrode 106 and the bottom electrode 102.

As further illustrated in FIGS. 1A and 1B, the first and second MTJdevices 110 a and 110 b each have an oval shape with substantially samedimensions. The first and second MTJ devices 110 a and 110 b areoriented such that the major axes of the oval shapes are substantiallyparallel to an easy axis 180.

Further, the first and second MTJ devices 110 a and 110 b each have asandwich structure including two magnetic layers separated by atunneling layer. The first MTJ device 110 a includes a first pinnedlayer 112 a made of a magnetic material, such as NiFe, CoFe, CoFeB,etc., and formed on or over the bottom electrode 102. The first pinnedmagnetic layer 112 a has a first pinned magnetization 114 a, as shown inFIG. 1B, substantially parallel to a first pinned direction 140, whichmay form an angle of about 45 degrees or 135 degrees to the easy axis180. In some examples, the 45 or 135 degree angle may vary within, forexample, a ±3%, ±5%, ±10%, or ±15% range, depending on various factors,such as design specifications, applications of the sensor, manufacturingprocess, or control process, etc. A first tunneling layer 115 a of anon-magnetic material, such as AlO, MgO, etc., may be formed on or overthe first pinned layer 112 a. A first free magnetic layer 116 a made ofa similar magnetic material is formed on or over the first tunnelinglayer 115 a and has a first free magnetization 118 a substantiallyparallel to the easy axis 180. The top electrode 106 connectsconductively to the first free magnetic layer 116 a.

The second MTJ device 110 b has a substantially similar structure as thefirst MTJ devices 110 a. The second MTJ device 110 b includes a secondpinned layer 112 b made of a magnetic material similar to that of thefirst pinned layer 112 a and formed on or over the bottom electrode 102.The second pinned layer 112 b has a second pinned magnetization 114 bthat is also substantially parallel to the first pinned direction 140. Asecond tunneling layer 115 b of a non-magnetic material is formed on orover the second pinned layer 112 b. A second free magnetic layer 116 bof the magnetic material is formed on or over the second tunneling layer115 b and has a second free magnetization 118 b that is also initiallyand substantially parallel to the easy axis 180. The top electrode 106connects conductively to the second free magnetic layer 116 b.

As shown in FIG. 1B, a conductive wire 108 may be arranged to cross thefirst and second MTJ devices 110 a, 110 b. In some examples, theconductive wire 108 can be placed in various locations or layers. Forexample, the conductive wire 108 may be disposed above or below the topelectrode 106, or above or below the bottom electrode 102. A set current(or setting current) I_(SET) may flow in the conductive wire 108 togenerate ampere fields for the MS-TMR 100. The conductive wire 108 isarranged so that it is substantially perpendicular to the easy axis 180while crossing the first and second MTJ devices 110 a and 110 b. Theampere fields at the locations of the first and second MTJ devices 110 aand 110 b are substantially parallel to the easy axis 180, but are insubstantially opposite directions. The ampere fields generated by theset current I_(SET) are used to set the directions of the first andsecond free magnetizations 118 a and 118 b, which may be substantiallyparallel to the easy axis 180 and are in substantially oppositedirections. In some examples, in the conductive wire 108, the sectionsthat cross the first and second MTJ devices 110 a and 110 b may or maynot be substantially perpendicular to the easy axis 180.

Although FIG. 1B depicts that the conductive wire 108 forms a U shape,the conductive wire 108 may form a variety of shapes or arranged inother proper forms. In some embodiments, the conductive wire 108 may beintegrated with or formed as a part of the top electrode 106 or thebottom electrode 102.

The first and second free magnetizations 118 a and 118 b are depicted intheir initial states, when the MS-TMR 100 is not subject to an externalmagnetic field. In some embodiments, the set current I_(SET) forgenerating the ampere fields may be turned on for a period of time andthen turned off to set the first and second free magnetizations 118 aand 118 b to their initial states before MS-TMR 100 is used to sense theexternal magnetic field. The set current I_(SET) may be supplied by anexternal circuit known in the art. The value of the set current and thelength of the time period required to set the free magnetizations mayvary depending on the design of the MS-TMR 100.

The first and second pinned magnetizations 114 a and 114 b may be setduring an annealing process when the MS-TMR 100 is formed. The annealingprocess is described in greater details below. The MS-TMR 100 issuitable for detecting and measuring an external field, which issubstantially perpendicular to the easy axis 180 and substantiallyparallel to the plane of the MS-TMR 100.

When an external magnetic field is applied to the MS-TMR 100, theorientations of the first and second pinned magnetizations 114 a and 114b do not change, while the first and second free magnetizations 118 aand 118 b may be rotated in the plane of the first and second freemagnetic layers 116 a and 116 b. The conductivity of the MS-TMR 100between the top electrode 106 and the bottom electrode 102 may depend onthe relative angles between the first and second pinned magnetizations114 a and 114 b and the first and second free magnetizations 118 a and118 b and is described below with reference to FIGS. 2A and 2B.

FIG. 2A illustrates rotations of the first and second freemagnetizations 118 a and 118 b of the MS-MTR 100, when an externalmagnetic field 402 is applied to the MS-TMR 100, consistent with thedisclosed embodiments. The external magnetic field 402 is substantiallyperpendicular to the easy axis 180 of the first and second MTJ devices110 a and 110 b and substantially parallel to the plane of the substrate90 or the plane of the MS-TMR 100. As a result of the external magneticfield 402, the first free magnetization 118 a of the first MTJ device110 a and the second free magnetization 118 b of the second MTJ device110 b are rotated by an angle θ counterclockwise and clockwise,respectively, as illustrated in FIG. 2A.

Accordingly, the conductivity G_(π/4) of the first MTJ device 110 a andthe conductivity G_(3π/4) of the second MTJ device 110 b can becalculated as follows:

$\begin{matrix}{\begin{matrix}{G_{\pi/4} = {\frac{G_{P}}{2}\left\lbrack {1 + \frac{1 + {{MR}\;{\cos\left( {\frac{\pi}{4} + \theta} \right)}}}{1 + {MR}}} \right\rbrack}} \\{{= {\frac{G_{P}}{2}\left\lbrack {1 + \frac{1 + {\frac{MR}{\sqrt{2}}\left( {{\cos\;\theta} - {\sin\;\theta}} \right)}}{1 + {MR}}} \right\rbrack}},}\end{matrix}{and}} & (1) \\\begin{matrix}{G_{3{\pi/4}} = {\frac{G_{P}}{2}\left\lbrack {1 + \frac{1 + {{MR}\;{\cos\left( {\frac{3\pi}{4} + \theta} \right)}}}{1 + {MR}}} \right\rbrack}} \\{{= {\frac{G_{P}}{2}\left\lbrack {1 + \frac{1 + {\frac{MR}{\sqrt{2}}\left( {{{- \cos}\;\theta} - {\sin\;\theta}} \right)}}{1 + {MR}}} \right\rbrack}},}\end{matrix} & (2)\end{matrix}$where θ is the rotation angle of the first free magnetization 118 a andthe second free magnetization 118 b when the external magnetic field 402is applied, MR represents the magneto-resistance ratio of the first MTJdevice 110 a and the second MTJ device 110 b, which are substantiallyidentical, G_(p) is the conductivity of the first and second MTJ devices100 a and 100 b when the first and second free magnetizations 118 a and118 b are substantially parallel to the first and second pinnedmagnetizations 114 a and 114 b.

The conductivity of the MS-TMR 100 is the result of the first and secondMTJ devices 110 a and 110 b connected or coupled in parallel between thetop and bottom electrodes 106 and 102. Accordingly, the conductivity ofthe MS-TMR 100, when the external magnetic field 402 is applied, can becalculated as follows:

$\begin{matrix}\begin{matrix}{G = {G_{\pi/4} + G_{3\;{\pi/4}}}} \\{= {{G_{P}\left\lbrack {1 + \frac{1 - {\frac{MR}{\sqrt{2}} \times \sin\;\theta}}{1 + {MR}}} \right\rbrack}.}}\end{matrix} & (3)\end{matrix}$FIG. 2B depicts, as functions of the rotation angle θ, the generaltrends of the conductivity G of the MS-MTR 100, the conductivity G_(π/4)of the first MTJ device 110 a, the conductivity G_(3π/4) of the secondMTJ device 110 b, and the conductivity G_(π/2) of a conventional TMR.

In some embodiments, when the external magnetic field 402 is smallerthan the coercivity H_(C) of the first and second MTJ devices 110 a and110 b, the following relationship holds:

${{\sin\;\theta} \cong \frac{H_{\bot}}{H_{C}}},$where H_(⊥) is the intensity of the external magnetic field 402. As aresult, by applying the above equation to Eq. (3), the external magneticfield 402 can be measured by solving the following linear relationshipEq. (4) for H_(⊥):

$\begin{matrix}{G = {{G_{P}\left\lbrack {1 + \frac{1 - {\frac{MR}{\sqrt{2}}\frac{H_{\bot}}{H_{C}}}}{1 + {MR}}} \right\rbrack}.}} & (4)\end{matrix}$

FIG. 3A illustrates another MS-TMR 150 generally corresponding to theMS-TMR 100 described above. In this embodiment, the first and second MTJdevices 110 a and 110 b each have substantially same oval shapes. Amajor axis of the oval shape has a length of substantially 2 microns,and a minor axis of the oval shape has a length of substantially 1micron. The first and second free magnetic layers 116 a and 116 b havesubstantially same thicknesses, which is about 10 angstroms (Å), asaturation magnetization M_(s) is substantially 1000 emu/cc, and ananisotropy constant K_(u) is 800 erg/cc. An external magnetic field 502is applied to the MS-TMR 150, substantially perpendicular to the easyaxis 180 and substantially parallel to the plane of the first and secondMTJ devices 110 a and 110 b. As a result, the first free magnetization118 a of the first MTJ device 110 a and the second free magnetization118 b of the second MTJ device 110 b are rotated counterclockwise andclockwise, respectively, by an angle θ.

FIG. 3B illustrates, as functions of the external magnetic field 502,the simulated values of the conductivity G of the MS-MTR 150, theconductivity G_(π/4) of the first MTJ device 110 a, and the conductivityG_(3π/4) of the second MTJ device 110 b according to Eqs. (1), (2), and(3). As shown in FIG. 3B, the conductivity G of the MS-TMR 150approximately linearly decreases as the external magnetic fieldincreases. According to another embodiment, when the first and secondpinned magnetizations 114 a and 114 b are reversed, the approximatelylinear relationship between the external magnetic field 502 and theconductivity G is reversed, accordingly. As a result, the conductivityof the MS-TMR 150 linearly increases as the external magnetic field 502increases.

FIG. 4 illustrates a top-view of a two-axis magnetic field sensor 250disposed on a single substrate or separate substrates, according toanother embodiment of the disclosure. The two-axis magnetic field sensor250 is presented in an X-Y coordinate for easy of reference, and can beused to sense the components along the X axis and the Y axis of anexternal magnetic field, simultaneously.

The two-axis magnetic field sensor 250 includes an X-axis magnetic fieldsensor 250 a and a Y-axis magnetic field sensor 250 b. The X-axismagnetic field sensor 250 a and the Y-axis magnetic field sensor 250 bgenerally correspond to the MS-TMR 100 depicted in FIGS. 1A and 1B.Accordingly, the same reference numerals refer to like elements. TheX-axis magnetic field sensor 250 a comprises a first MS-TMR 100 having afirst easy axis 180 substantially parallel to the Y axis, a first pinneddirection 140, and a first conductive wire 108. The Y-axis magneticfield sensor 250 b comprises a second MS-TMR 200 having a second easyaxis 280 substantially parallel to the X axis, a second pinned direction240, and a second conductive wire 208. The first and second pinneddirections 140 and 240 are both substantially parallel to a bisectiondirection 350, which evenly divides a section between the X axis and theY axis. As a result, the bisection direction 350 forms an angle of about45 degrees or 135 degrees with the X axis and the Y axis, respectively.

The first MS-TMR 100 and the second MS-TMR 200 have similar structuresas the MS-TMR shown in FIGS. 1A and 1B. The planes of the first MS-TMR100 and the second MS-TMR 200 are both parallel to the surface of thesubstrate. The first MS-TMR 100 includes a first MTJ device 110 a havinga first pinned magnetization 114 a and a first free magnetization 118 a.The first MS-TMR 100 further includes a second MTJ device 110 b having asecond pinned magnetization 114 b and a second free magnetization 118 b.The first and second pinned magnetizations 114 a and 114 b aresubstantially parallel to the first pinned direction 140. The first andsecond free magnetizations 118 a and 118 b are initially andsubstantially parallel to the first easy axis 180 but are insubstantially opposite directions.

The second MS-TMR 200 includes a third MTJ device 210 a having a thirdpinned magnetization 214 a and a third free magnetization 218 a. Thesecond MS-TMR 200 further includes a fourth MTJ device 210 b having afourth pinned magnetization 214 b and a fourth free magnetization 218 b.The third and fourth pinned magnetizations 214 a and 214 b aresubstantially parallel to the second pinned direction 240. The third andfourth free magnetizations 218 a and 218 b are initially parallel to thesecond easy axis 280, but in substantially opposite directions.

Similar to the magnetic field sensor 10 depicted in FIGS. 1A and 1B, theX-axis magnetic field sensor 250 a may sense an external magnetic fieldcomponent along the X-axis, which is perpendicular to the first easyaxis 180 and parallel to the plane of the substrate of the magneticfield sensor 250. Simultaneously, the Y-axis magnetic field sensor 250 bmay sense an external magnetic field component along the Y-axis, whichis perpendicular to the second easy axis 280 and parallel to the planeof the substrate of the magnetic sensor 250.

FIGS. 5A-5C depict another magnetic field sensor 300 for sensing anexternal magnetic field along a Z-axis, which is perpendicular to thebase plane 360 of the substrate 390, according to another embodiment.FIG. 5A depicts a top view of the magnetic field sensor 300, in whichthe Z axis is perpendicular to the base plane 360 of the substrate 390and pointing upwards. The magnetic field sensor 300 is formed on thesubstrate 390, having a first inclined surface 360 a and a secondinclined surface 360 b. The first inclined surface 360 a and the secondinclined surface 360 b each form a bevel angle with the base plane 360,while the first inclined surface 360 a and the second inclined surface360 b are formed symmetrically with respect to a medial axis 305 of thebase plane 360.

Furthermore, the magnetic field sensor 300 has a first TMR 310 formed onthe first inclined surface 360 a and a second TMR 320 formed on thesecond inclined surface 360 b. The first TMR 310 and the second TMR 320each have a MTJ device similar to the first and second MTJ device 110 aand 110 b depicted in FIGS. 1A and 1B.

FIG. 5B illustrates a cross-sectional view of the magnetic field sensor300 of FIG. 5A, according to one embodiment. As shown in FIG. 5B, thesubstrate 390 has a groove structure 370 a. The first and second TMRs310 and 320 are formed on the inside of the first and second inclinedsurfaces 360 a and 360 b of the groove structure 370 a. As a result, thefirst and second TMRs 310 and 320 face towards each other.

Alternatively, as shown in FIG. 5C, which illustrates a cross-sectionalview of the magnetic field sensor 300 of FIG. 5A, according to anotherembodiment. In FIG. 5C, the substrate 390 has a dike structure 370 b, inwhich the first and second TMRs 310 and 320 are formed on the outside ofthe first and second inclined surfaces 360 a and 360 b. As a result, thefirst and second TMRs 310 and 320 face away from each other.

As further shown in FIG. 5A, the first and second TMRs 310 and 320 havesubstantially similar structures. The first TMR 310 has a first freemagnetization 318 initially parallel to the first easy axis 380 a, and afirst pinned magnetization 314 parallel to the first pinned direction340 a (shown in FIG. 5B, for example). The first easy axis 380 a issubstantially parallel to the medial axis 305, and the first pinneddirection 340 a is substantially perpendicular to the first easy axis380 a and parallel to the first inclined surface 360 a. The second TMR320 has a second free magnetization 328 initially parallel to the secondeasy axis 380 b, and a second pinned magnetization 324 parallel to thesecond pinned direction 340 b (shown in FIG. 5B, for example). Thesecond easy axis 380 b is also substantially parallel to the medial axis305, and the second pinned direction 340 b is substantiallyperpendicular to the second easy axis 380 b and parallel to the secondinclined surface 360 b.

The first and second pinned directions 340 a and 340 b are parallel totheir respective first and second inclined surfaces 360 a and 360 b andpoint generally towards the negative direction of the Z axis (shown inFIGS. 5B and 5C). Alternatively, the first and second pinned directions340 a and 340 b may be parallel to their respective first and secondinclined surfaces 360 a and 360 b and point generally towards thepositive direction of the Z axis. Because the pinned direction of eachTMR is substantially perpendicular to the respective easy axis, thefirst and second free magnetizations 318 and 328 are in substantiallythe same direction or opposite directions, when there is no externalmagnetic field.

The first TMR 310 has a magnetic field sensing direction substantiallyperpendicular to the first easy axis 380 a and parallel to the firstinclined surface 360 a. Likewise, the second TMR 320 has a magneticfield sensing direction substantially perpendicular to the second easyaxis 380 b and parallel to the second inclined surface 360 b. The firstand second pinned directions 314 and 324 are set by applying a magneticfield substantially perpendicular to the base plane 360 of the substrate390 during an anneal process.

When an external magnetic field is applied to the magnetic field sensor300, the fast TMR 310 and the second TMR 320 together sense the magneticfield component along the Z axis. The first and second freemagnetizations 318 and 328 rotate in response to the external magneticfield, thereby changing the conductivity of the magnetic field sensor300. Thus, magnetic field component along the Z axis may be determinedbased on the conductivity of the magnetic field sensor 300.

The magnetic field sensor 300 of FIG. 5A is further described below withreference to FIGS. 6A and 6B, which depict a coordinate transformationfor the magnetic field sensor 300. The coordinate transformationtransforms the first and second inclined surfaces 360 a and 360 b from aglobal X-Y-Z coordinate system to their respective A-B-C coordinatesystems.

As shown in FIG. 6A, the global X-Y-Z coordinate system of the substrateis defined as follows: a Z axis is perpendicular to the base plane 360of the substrate 390 and the X-Y plane is parallel to the base plane 360of the substrate 390. For each of the first or second inclined surfaces360 a and 360 b of the substrate 390, an A-D-Z coordinate system isfurther defined as follows: the Z axis is still the original Z axis, anA axis is perpendicular to the Z axis and is substantially parallel tothe medial axis 305 on the base plane 360 of the substrate 390, and a Daxis is perpendicular to the A and Z axes and forms an azimuth angle αwith the X axis. Furthermore, as shown in a cross-sectional view in FIG.6B for the first and second inclined surfaces 360 a and 360 b, a B axisis defined to be substantially parallel to the respective first andsecond inclined surface 360 a and 360 b and forms a bevel angle β withthe respective A-D plane. A C axis is normal to the respective first andsecond inclined surfaces 360 a and 360 b. Therefore, an externalmagnetic field can be represented by magnetic field components along theA, B, and C axes.

Furthermore, an external magnetic field in the global X-Y-Z coordinatesystem can be represented by a linear combination of the magnetic fieldcomponents along the respective A, B, and C axes. When the magneticfield sensor 300 is placed in the external magnetic field, the first TMR310 and the second TMR 320 sense the magnetic field components alongtheir respective B axes, which are parallel to their respective firstand second inclined surfaces 360 a and 360 b. As a result, when thefirst TMR 310 and the second TMR 320 are connected in parallel, thecontributions to the conductivity by the magnetic field components alongthe X axis and Y axis cancel out each other, while the contributions bythe magnetic field components along the Z axis add together. Hence, themagnetic field component along the Z axis may be determined based on theconductivity of the magnetic field sensor 300.

When an external magnetic field is applied to the magnetic field sensor300 as shown in FIG. 5A, the conductivities G_(L) and G_(R) of the firstand second TMRs 310 and 320 can be calculated from Eq. (5) and Eq. (6),respectively, as follows:

$\begin{matrix}{{G_{L} = {\frac{G_{P}}{2}\left\lbrack {1 + \frac{1 + {\frac{MR}{H_{C}}\left( {{H_{X}\cos\;\alpha\;\cos\;\beta} + {H_{Y}\sin\;\alpha\;\cos\;\beta} - {H_{Z}\sin\;\beta}} \right)}}{1 + {MR}}} \right\rbrack}},\mspace{20mu}{and}} & (5) \\{{G_{R} = {\frac{G_{P}}{2}\left\lbrack {1 + \frac{1 - {\frac{MR}{H_{C}}\left( {{H_{X}\cos\;\alpha\;\cos\;\beta} + {H_{Y}\sin\;\alpha\;\cos\;\beta} + {H_{Z}\sin\;\beta}} \right)}}{1 + {MR}}} \right\rbrack}},} & (6)\end{matrix}$where G_(p), MR, H_(c), α and β are defined above, and H_(X), H_(Y), andH_(Z) are the magnetic field components along the X, Y, and Z axes. Themagnetic field component along the Z axis may be calculated from Eq. (7)as follows:

$\begin{matrix}\begin{matrix}{G = {G_{L} + G_{R}}} \\{= {{G_{P}\left( {1 + \frac{1 - {{MR}\frac{H_{Z}}{H_{C}}\sin\;\beta}}{1 + {MR}}} \right)}.}}\end{matrix} & (7)\end{matrix}$

FIG. 7 depicts a top view a Z-axis magnetic field sensor 700 disposed ona substrate 390 with a base plane 360. As shown in FIG. 7, the first TMR310 and second TMR 320 of FIG. 5A may be replaced with a first MS-TMR300 a and a second MS-TMR 300 b, respectively. FIG. 7 uses samereference numerals to refer to like elements as described above inconnection with FIG. 5A.

According to FIG. 7, the Z-axis magnetic field sensor 700 includes afirst MS-TMR 300 a and an a second MS-TMR 300 b disposed on,respectively, a first inclined surface 360 a and a second inclinedsurface 360 b of the substrate 390. The first and second inclinedsurfaces 360 a and 360 b may form a groove similar to that shown in FIG.5B or a dike structure similar to that shown in FIG. 5C. The firstinclined surface 360 a and the second inclined surface 360 b formsubstantially same bevel angles with the base plane 360. In addition,the first inclined surface 360 a and the second inclined surface 360 bare symmetrically disposed with respect to a medial axis 305 of the baseplane 360.

The first MS-TMR 300 a has a first pinned direction 340 a in the firstinclined surface 360 a, forming an angle of about 45 degrees or 135degrees with a first easy axis 380 a, which is substantially parallel tothe axis 305. The second MS-TMR 300 b has a second pinned direction 340b in the second inclined surface 360 b, forming an angle of about 45degrees or 135 degrees with a second easy axis 380 b, which is alsosubstantially parallel to the medial axis 305.

The first MS-TMR 300 a includes a first MTJ device 310 a and a secondMTJ device 310 b disposed on or over the first inclined surface 360 a.The first MTJ device 3100 a has a first free magnetization 318 a and afirst pinned magnetization 314 a. The second MTJ device 310 b has asecond free magnetization 318 b and a second pinned magnetization 314 b.The first and second pinned magnetizations 314 a and 314 b both aresubstantially parallel to the first pinned direction 340 a. The firstand second free magnetizations 318 a and 318 b are both initially andsubstantially parallel to the first easy axis 380 a and aresubstantially opposite to each other. In addition, the initialdirections of the first and second free magnetizations 318 a and 318 bmay be set by an ampere field generated by a set current flowing in aconductive wire 308. The first MTJ device 310 a and the second MTJdevice 310 b are disposed between a top electrode and a bottomelectrode, and have similar structures as those depicted in FIG. 1A.

Similarly, the second MS-TMR 300 b includes a third MTJ device 320 a anda fourth MTJ device 320 b disposed on or over the second inclinedsurface 360 b of the substrate. The third MTJ device 320 a has a thirdfree magnetization 328 a and a third pinned magnetization 324 a. Thefourth MTJ device 320 b has a fourth free magnetization 328 b and afourth magnetization 324 b. Likewise, the third and fourth pinnedmagnetizations 324 a and 324 b are both substantially parallel to asecond pinned direction 340 b. The third and fourth free magnetizations328 a and 328 b are both initially parallel to the second easy axis 380b and in substantially opposite directions, which are set by the amperefield generated by the current flowing in the wire 308. In addition, thethird MTJ device 320 a and the fourth MTJ device 320 b are disposedbetween a top electrode and a bottom electrode similar to those shown inFIG. 1A.

The Z-axis magnetic field sensor 700 is formed by coupling or connectingthe first and second MS-TMRs 300 a and 300 b in parallel. The topelectrodes of the first and second MS-TMRs 300 a and 300 b are connectedtogether, and the bottom electrodes of the first and the second MS-TMRs300 a and 300 b are connected together. The first easy axis and thesecond easy axis 380 a and 380 b are substantially parallel to a medialaxis 305 of the base plane 360 of the substrate 390. The first andsecond pinned directions 340 a and 340 b each form an angle of about 45degrees or 135 degrees with the respective easy axes 380 a and 380 b onor over the respective first and second inclined surfaces 360 a and 360b. When an external magnetic field is applied, the conductivity of theZ-axis magnetic field sensor 700 varies according to the magnetic fieldcomponent (H_(z)) along the Z axis. As a result, the Z-axis magneticfield component (H_(z)) may be sensed and determined through theconductivity of the Z-axis magnetic field sensor 700. The conductivityof the Z-axis magnetic field sensor 700 of FIG. 7 may be calculated byEq. (8).

$\begin{matrix}{{G = {2\;{G_{P}\left( {1 + \frac{1 - {\frac{MR}{\sqrt{2}}\frac{H_{Z}}{H_{C}}\sin\;\beta}}{1 + {MR}}} \right)}}},} & (8)\end{matrix}$where G_(p), MR, H_(c), H_(z), and β are defined above. Compared withexisting magnetic field sensors, the parallel connection of the firstMS-TMR 300 a and second MS-TMR 300 b in the Z-axis magnetic field sensor700 may allow the bevel angle β between the inclined surface (i.e.,first and second inclined surfaces 360 a and 360 b) and the based plane360 of the substrate 390 to be less than 45 degrees without compromisingthe ability to sensor the Z-axis magnetic component. As a result, thedimension of the Z-axis magnetic field sensor 700 may be reduced,thereby allowing easy integration into electronic devices forapplication systems, such as compass chips of GPS systems or mobilephones.

FIG. 8 depicts a top view of a three-axis magnetic field sensor 450disposed on a substrate 390 with a base plane 360, according to anotherembodiment. In FIG. 8, the three-axis magnetic field sensor 450 ispresented in an X-Y-Z coordinate system, in which the X-Y plane issubstantially parallel to the base plane 360, while the Z axis pointsupwards (i.e., towards a viewer) and perpendicular to the base plane360. The three-axis magnetic field sensor 450 includes, in an integratedform, a two-axis magnetic field sensor 250 as disclosed in FIG. 4 and aZ-axis magnetic field sensor 700 as disclosed in FIG. 7. For ease ofunderstanding, the same reference numerals are used to refer to likeelements in FIG. 8.

The two-axis magnetic field sensor 250 further includes an X-axismagnetic field sensor 250 a having a first MS-TMR 100 and a Y-axismagnetic field sensor 250 b having a second MS-TMR 200. The first MS-TMR100 has a first easy axis 180 substantially parallel to the Y axis and afirst pinned direction 140 substantially parallel to the bisectiondirection 350 of the X-Y plane, which evenly divides the angle betweenthe X and Y axes. The second MS-TMR 200 has a second easy-axis 280substantially parallel to the X-axis and a second pinned direction 240also substantially parallel to the bisection direction 350. The plane ofthe first MS-TMR 100 is parallel to the base plane 360 and the sensingdirection is perpendicular to first easy axis 180 and along the X axis.The plane of the second MS-TMR 200 is parallel to the base plane 360 andthe sensing direction is perpendicular to second easy axis 280 and alongthe Y axis.

The Z-axis magnetic field sensor 300 includes two MS-TMRs (i.e., a thirdMS-TMR 300 a and a fourth MS-TMR 300 b) disposed on or over the firstand second inclined surfaces 360 a and 360 b of the substrate 390. Thefirst inclined surface 360 a and the second inclined surface 360 b formsubstantially same bevel angles with the base plane 360. The firstinclined surface 360 a and the second inclined surface 360 b aresymmetrically formed with respect to a medial axis 305 of the X-Y plane,in which the medial axis 305 is parallel to the bisection direction 350.The third MS-TMR 300 a has a third easy axis 380 a and a third pinneddirection 340 a, and the fourth MS-TMR 300 b has an fourth easy axis 380b and a fourth pinned direction 340 b. The third easy axis 380 a and thefourth easy axis 380 b are substantially parallel to the medial axis305. The third and fourth pinned directions 340 a and 340 b are in therespective first and second inclined surfaces 360 a and 360 b and forman angle of about 45 degrees or 135 degrees with the third and fourtheasy axes 380 a and 380 b, respectively.

As further shown in FIG. 8, the first MS-TMR 100 has a first MTJ device110 a with a first free magnetization 118 a and a first pinnedmagnetization 114 a and a second MTJ device 110 b with a second freemagnetization 118 b and a second pinned magnetization 114 b. The firstand second pinned magnetizations 114 a and 114 b are substantiallyparallel to the first pinned direction 140. The first and second freemagnetizations 118 a and 118 b are initially parallel to the first easyaxis 180 and are set to substantially opposite directions. The secondMS-TMR 200 has a third MTJ device 210 a with a third free magnetization218 a and a third pinned magnetization 214 a and a fourth MTJ device 210b with a fourth free magnetization 218 b and a fourth pinnedmagnetization 214 b. The third and fourth pinned magnetizations 214 aand 214 b are substantially parallel to the second pinned direction 240.The third and fourth free magnetizations 218 a and 218 b are initiallyparallel to the second easy axis 280 and are set to substantiallyopposite directions. As a result, the first and second pinnedmagnetizations 114 a and 114 b each form an angle of about 45 degrees or135 degrees with the respective the first and second free magnetizations118 a and 118 b. Similarly, the third and fourth pinned magnetizations214 a and 214 b each form an angle of about 45 degrees or 135 degreeswith the respective third and fourth free magnetizations 218 a and 218b.

The third MS-TMR 300 a has a fifth MTJ device 310 a with a fifth freemagnetization 318 a and a fifth pinned magnetization 314 a and a sixthMTJ device 310 b with a sixth free magnetization 318 b and a sixthpinned magnetization 314 b. The fifth and sixth pinned magnetizations314 a and 314 b are both substantially parallel to the third pinneddirection 340 a. The fifth and sixth free magnetizations 318 a and 318 bare initially parallel to the third easy axis 380 a and are set tosubstantially opposite directions. The fourth MS-TMR 300 b has a seventhMTJ device 320 a with a seventh free magnetization 328 a and a seventhpinned magnetization 324 a and an eighth MTJ device 320 b with an eighthfree magnetization 328 b and an eighth pinned magnetization 324 b. Theseventh and eighth pinned magnetizations 324 a and 324 b are bothsubstantially parallel to the fourth pinned direction 340 b. The seventhand eighth free magnetizations 328 a and 328 b are initially parallel tothe fourth easy axis 380 b and are set to substantially oppositedirections. As a result, the fifth and sixth pinned magnetizations 314 aand 314 b each form an angle of about 45 degrees or 135 degrees with therespective fifth and sixth free magnetizations 318 a and 318 b.Similarly, the seventh and eighth pinned magnetizations 324 a and 324 beach form an angle of about 45 degrees or 135 degrees with therespective seventh and eighth free magnetizations 328 a and 328 b.

As described above in connection with FIGS. 4 and 7, each magnetic fieldsensor also has a respective conductive wire for flowing the set currentto generate an ampere field therein and set the initial orientation ofthe respective free magnetization. For easy of illustration, theconductive wires are not shown in FIG. 8.

When the three-axis magnetic field sensor 450 is subjected to anexternal magnetic field, the components of the external magnetic fieldalong the X, Y, and Z axes may be sensed simultaneously in consistencewith the embodiments disclosed herein.

FIG. 9 is a schematic diagram for setting the pinned magnetization ofeach MS-TMR of the magnetic field sensors, as depicted in FIGS. 1A-8, byapplying a single slantwise magnetic field or dual magnetic fieldsduring an annealing process, consistent with disclosed embodiments.According to one embodiment, as shown in FIG. 9, the three-axis magneticfield sensor 450 of FIG. 8 is presented in an X-Y-Z coordinate system asdescribed above. A slantwise field 400, which forms a zenith angle γwith the Z axis, is applied to the three-axis magnetic field sensor 450during the annealing process. Furthermore, the slantwise field 400 ispositioned so that the projection of the slantwise field 400 in the X-Yplane is substantially parallel to the bisection direction 350 and formsan azimuth angle α of about 45 degrees with the X and Y axes,respectively. As a result, the first and second pinned directions 140and 240 of the first and second MS-TMRs 100 and 200 are set to besubstantially parallel to the bisection direction 350.

The zenith angle γ is set according to the bevel angle β between theinclined surface (i.e., the first and second inclined surfaces 360 a and360 b) and the base plane 360 of the substrate 390 as shown in FIG. 6B.The zenith angle γ may be calculated according to Eq. (9) as follows:γ=tan⁻¹(sin β).  (9)

For example, when the bevel angle β=54°, the azimuth angles α=45° andthe zenith angles γ=39° for the slantwise field 400. Accordingly, theprojections of the slantwise field 400 onto the first and secondinclined surfaces 360 a and 360 b form an angle of about 45 degrees or135 degrees with the third and fourth easy axes 380 a and 380 b,respectively. As a result of the slantwise field 400, the third and thefourth pinned directions 340 a and 340 b are set to be substantiallyparallel to the projections of the slantwise field 400 on the first andsecond inclined surfaces 360 a and 360 b, respectively. According to afurther embodiment, for an anneal instrument with a single magneticfield generator, the azimuth and zenith angles may be set by physicallyrotating and tilting the three-axis magnetic field sensor 450 withrespect to the magnetic field 400 so as to achieve the desired anglesfor the pinned magnetization as described herein.

According to another embodiment as further shown in FIG. 9, a dual fieldannealing process may be used to set the pinned magnetizations byapplying a zenith magnetic field 420 and an azimuth magnetic field 440to the three-axis magnetic field sensor 450. The zenith magnetic field420 is substantially parallel to the Z axis, and the azimuth magneticfield 440 is substantially parallel to the X-Y plane along the bisectiondirection 350. The zenith magnetic field 420 and the azimuth magneticfield 440 have a relationship described by Eq. (10) as follows:H _(AZ) =H _(Z) sin β,  (10)The dual field annealing process may be performed by an annealinstrument having a horizontal first magnetic field generator 1102 and avertical second magnetic field generators 1104. In the dual fieldannealing process, the mechanical manipulation (e.g., tilting androtating) of the three-axis magnetic field sensor 450 may be replaced byelectronic signal controlling of the horizontal first magnetic fieldgenerator 1102 and the vertical second magnetic field generator 1104.Accordingly, the pinned magnetization of each MS-TMR can be set bysimultaneously applying the azimuth magnetic field 440 and the zenithmagnetic field 420, which are generated by the horizontal first andvertical second magnetic field generators 1102 and 1104. The intensityof the zenith magnetic field 420 and the azimuth magnetic field 440 isset by the generators so that a vector summation of the zenith magneticfield 420 and the azimuth magnetic field 440 is equivalent to theslantwise field 400 described above.

According to the above embodiment, the pinned magnetization of a MS-TMRdisposed on the inclined surface may be set based on the bevel angle ofthe inclined surface. Accordingly, the magnetic field sensors describedabove allow for a wider range of the bevel angle of the inclinedsurfaces. The actual angles between the pinned magnetizations and theirrespective easy axis of a MS-TMR may deviate from 45 degrees or 135degrees after the annealing process. For example, the deviation may becaused by the easy axis deflection resulted from MTJ pattern shapedistortions, variations of the zenith and azimuth angles of theslantwise field, or a quantity tolerance of the zenith and azimuthmagnetic field. Accordingly, the angle between the pinned direction andthe easy axis may vary between about 40 to 50 degrees, between about 35to 55 degrees, between about 130 to 140 degrees, or between about 125 to145 degrees. Nevertheless, the magnetic field sensors described abovecan still properly respond to the external magnetic fields with thedeviations of the angle between the pinned direction and the easy axis.

According to another embodiment of the disclosure, the magnetic fieldsensors described above may be integrated with a CMOS sensing circuitand fabricated together with the CMOS sensing circuit. FIG. 10illustrates a circuit diagram of a magnetic field sensing circuit 500for sensing an external magnetic field and converting the externalmagnetic field into electronic signals. The magnetic field sensingcircuit 500 includes a first magnetic field sensor 510 and a secondmagnetic field sensor 520. The second magnetic field sensor 520 providesmeasurements of the external magnetic field, while the first magneticfield sensor 510 provides a zero-field reference to the magnetic fieldsensing circuit 500. The first and second magnetic field sensors 510 and520 have substantially same configurations and may be any magnetic fieldsensor described above. In addition, unlike the traditional Wheatstonebridge circuit for TMR magnetic field sensors, no shielding is requiredfor the magnetic field sensing circuit 500.

In the beginning of sensing an external magnetic field, a set current ispassed through the respective conductive wires 518 and 528 of the firstand second magnetic field sensors 510 and 520 to generate ampere fieldsin the first and second magnetic field sensors 510 and 520 to restoretheir respective free magnetizations to an initial state, so that thefree magnetizations of each of the first and second magnetic fieldsensors 510 and 520 are substantially parallel with the respective easyaxis and in substantially opposite directions. Thereafter, the setcurrent in the conductive wire 518 is maintained, while the set currentin the conductive wire 528 turned off. As a result, the freemagnetizations of the first magnetic field sensor 510 are kept or lockedat the initial state and not affected by any external magnetic field.Hence, the first magnetic field sensor 510 reflects a zero-field statusand provides the zero-field reference. On the other hand, the freemagnetizations of the second magnetic field sensor 520 may be affectedby the external magnetic field so that the second magnetic field sensor520 may sense the external magnetic field.

As shown in FIG. 10, in addition to the first and second magnetic fieldsensors 510 and 520, the magnetic field sensing circuit 500 includes abias voltage unit 502, a clamp voltage current mirror unit 504, and asignal transferring and amplifying unit 506. The bottom electrode of thezero-field reference of the first magnetic field sensor 510 and thebottom electrode of the second magnetic field sensor 520 are connectedto a node C. The top electrode of the zero-field reference of the firstmagnetic field sensor 510 is connected to a node D, and the topelectrode of the second magnetic field sensor 520 is connected to a nodeE.

As further shown in FIG. 10, the bias voltage unit 502 includes avoltage dividing branch, a voltage subtraction circuit, and a voltagesource V_(M). The voltage dividing branch includes four resistors Rconnected in series between a power voltage VDD and a ground voltageGND. As a result, the voltages at node A and node B are V_(A)=VDD/2 andV_(B)=VDD/4, respectively. The subtraction circuit includes anoperational amplifier OP1 having a positive input coupled to the node B.A resistor R is connected between a negative input and an output of theamplifier OP1. Another resistor R is connected between the negativeinput of the amplifier OP1 and the voltage source V_(M). Accordingly,the output voltage of the amplifier OP1 at node C is V_(C)=V_(A)−V_(M).Hence, the voltages across the MTJ devices of the zero-field referenceof the first magnetic field sensor 510 and the second magnetic fieldsensor 520 are biased at the voltage V_(M) therein.

The clamp voltage current mirror unit 504 includes a current mirror anda voltage clamper. The current mirror includes a first PMOS transistorQ1 and a second PMOS transistor Q2. The sources of the transistor Q1 andthe transistor Q2 are both connected to the voltage VDD. The drain ofthe transistor Q1 is connected to the node D, the drain of thetransistor Q2 is connected to a node E, and the gate of the transistorQ1 connects to the gate of the transistor Q2. The voltage clamperincludes an operational amplifier OP2 having a positive input connectedto the node A, and a negative input connected to the node D. The outputof the amplifier OP2 is connected to the gates of the transistors Q1 andQ2. The drain current of the second PMOS transistor Q2 is a mirror ofthe drain current of the first PMOS transistor Q1, wherein the draincurrent of the first PMOS transistor Q1 is equal to the current of thezero-field reference of the first magnetic field sensor 510.

The signal transfer amplifying unit 506 includes an operationalamplifier OP3 having a negative input connected to the node E and apositive input connected to the node A. A resistor R_(M) is connectedbetween the node E and the output of the operational amplifier OP3. Thepower of the operational amplifiers OP1, OP2, and OP3 are provided by asingle voltage VDD. The output of amplifier OP2 is fed back to thenegative input of amplifier OP2 via the transistor Q1. The output ofamplifier OP3 is fed back to the negative input of amplifier OP3 via theresistor R_(M). As a result, the voltages at the negative inputs ofamplifiers OP2 and OP3 are substantially equal to the voltages at therespective positive inputs, and the voltages at nodes D and E areclamped to the voltage of node A and equal to VDD/2.

At the node E, the current flowing into the second magnetic field sensor520 is a sum of the current flowing out from the drain of the secondPMOS transistor Q2 and a current flowing through the output of theoperational amplifier OP3 via the resistor R_(M). Therefore, the currentof the second magnetic field sensor 520 in substantially equal to a sumof the current of the zero-field reference of the first magnetic fieldsensor 510 and a sensed current due to the conductivity change of thesecond magnetic field sensor 520 caused by the external magnetic field.The output voltage of the operational amplifier OP3 (i.e., the outputvoltage V_(OUT) of signal transfer amplifying unit 506) is equal to thesum of the voltage at node E (i.e., VDD/2) and the voltage across theresistor R_(M). The voltage across the resistor R_(M) is the product ofthe sensed current multiplied by the resistance value of the resistorR_(M), and the sensed current is equal to the product of the biasvoltage V_(M) and the conductivity change ΔG of the second magneticfield sensor 520.

As a result, the output voltage V_(OUT) of the signal transferamplifying unit 506 is one half of the voltage VDD, when there is noexternal magnetic field. This design provides a full range of signalamplification and is favorable for a subsequent Analog-to-DigitalConvert (ADC) that is used to convert the output signal V_(OUT) to adigital form.

When the second magnetic field sensor 520 is subject to an externalmagnetic field, the output voltage V_(OUT) of the signal transferamplifying unit 506 is the sum of one half of the voltage VDD and thevoltage across the resistor R_(M). According to a further embodiment,the value of resistor R_(M) may be arranged to optimize the range of theoutput voltage V_(OUT) in according with the specification of thesubsequent ADC.

As described above, the sensing circuit depicted in FIG. 10 can be usedfor sensing magnetic fields along the X, Y, and Z axes when thecorresponding X, Y, and Z-axis magnetic field sensors are incorporatedinto the circuit. The back-end fabrication process of the first andsecond magnetic field sensors 510 and 520 can be integrated with thefront-end fabrication process of the sensing circuit depicted in FIG.10. The sensing circuit and the sensors may be integrated on the samesubstrate. Alternatively, the sensing circuit may also be separatelyfabricated, and may include other components. It should be noted thatthe bottom electrode and the top electrode in each MS-TMR describedabove for connecting the MTJ devices are not limited to the structuredescribed herein and may take other proper forms or implementations.

The embodiments disclosed herein provide a structure of a TunnelingMagneto-Resistor (TMR) and a method for sensing magnetic fields. Thedisclosed TMR structures and methods greatly reduce the complexity andthe cost of manufacturing magnetic sensors and also improve sensitivityand accuracy of magnetic sensing.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structures,configurations and methods of the disclosed embodiments withoutdeparting from the scope or spirit of the disclosed embodiments. In viewof the foregoing descriptions, it is intended that the discloseembodiments cover their various modifications and variations consistentwith the claims.

What is claimed is:
 1. A magnetic sensor for sensing an externalmagnetic field, comprising: a first electrode and a second electrodedisposed over a substrate; a first magnetic tunneling junction and asecond magnetic tunneling junction conductively disposed between thefirst electrode and the second electrode and connected in parallelbetween the first electrode and the second electrodes, the firstmagnetic tunneling junction and the second magnetic tunneling junctionbeing arranged along a first easy axis of the magnetic sensor; the firstmagnetic tunneling junction including a first pinned layer having afirst pinned magnetization, a first free layer having a first freemagnetization, and a first tunneling layer between the first pinnedlayer and the first free layer; the second magnetic tunneling junctionincluding a second pinned layer having a second pinned magnetization, asecond free layer having a second free magnetization, and a secondtunneling layer between the second pinned layer and the second freelayer; the first free magnetization and the second free magnetizationbeing arranged substantially in parallel to the first easy axis and insubstantially opposite directions; and the first pinned magnetizationand the second pinned magnetization each forming an angle of about 45 or135 degrees with the first easy axis, wherein the substrate has a firstinclined surface, a second inclined surface, and a base plane, the firstinclined surface and the second inclined surface each forming arespective bevel angle with the base plane; the first magnetic tunnelingjunction and the second magnetic tunneling junction are disposed on thefirst inclined surface of the substrate between the first electrode andthe second electrode; and the magnetic sensor further comprising: athird magnetic tunneling junction and a fourth magnetic tunnelingjunction disposed on the second inclined surface of the substratebetween a third electrode and a fourth electrode, the third magnetictunneling junction and the fourth magnetic tunneling junction beingconnected in parallel and arranged along a second easy axis that issubstantially parallel to the first easy axis, wherein: the thirdmagnetic tunneling junction has a third free layer having a third freemagnetization and a third pinned layer having a third pinnedmagnetization; the fourth magnetic tunneling junction has a fourth freelayer having a fourth free magnetization and a fourth pinned layerhaving a fourth pinned magnetization; the third and fourth pinnedmagnetizations each form an angle of about 45 or 135 degrees with thesecond easy axis; the third and fourth free magnetizations are parallelto the second easy axis and in substantially opposite directions; and aconductive wire passes through the first, second, third, and fourthmagnetic tunneling junctions for carrying a set current to generate thefirst, second, third, and fourth free magnetizations therein.
 2. Themagnetic sensor of claim 1, wherein: the first magnetic tunnelingjunction and the second magnetic tunneling junction have substantiallysimilar oval shapes each having a major axis substantially parallel tothe first easy axis; and planes of the first magnetic tunneling junctionand the second magnetic tunneling junction are substantially parallel toa base plane of the substrate.
 3. The magnetic sensor of claim 1,further comprising: a first conductive wire passing through the firstmagnetic tunneling junction and the second magnetic tunneling junctionand carrying a current for setting the first and second freemagnetizations.
 4. The magnetic sensor of claim 1, wherein: the firstand second free magnetizations rotate within respective planes of thefirst magnetic tunneling junction and the second magnetic tunnelingjunction when an external magnetic field is applied to the magneticsensor; and a conductivity of the magnetic sensor changes in response tothe rotations of the first and the second free magnetizations.
 5. Themagnetic sensor of claim 4, wherein the first and the second freemagnetizations rotate in response to a first external magnetic field ora first external magnetic field component that is substantiallyperpendicular to the first easy axis and substantially parallel to abase plane of the substrate.
 6. The magnetic sensor of claim 5, whereinthe conductivity of the magnetic sensor changes substantially linearlyin response to the first magnetic field or the first magnetic fieldcomponent.
 7. The magnetic sensor of claim 1, further comprising: athird electrode and a fourth electrode; and a third magnetic tunnelingjunction and a fourth magnetic tunneling junction disposed between thethird electrode and the fourth electrode and connected in parallelbetween the third electrode and the fourth electrode, the third magnetictunneling junction and the fourth magnetic tunneling junction beingarranged along a second easy axis that is substantially perpendicular tothe first easy axis, wherein: the third magnetic tunneling junction hasa third pinned magnetization and a third free magnetization; the fourthmagnetic tunneling junction has a fourth pinned magnetization and afourth free magnetization; the third and fourth pinned magnetizationseach form an angle of about 45 or 135 degrees with the second easy axis;and the third and fourth free magnetizations are parallel to the secondeasy axis and in substantially opposite directions.
 8. The magneticsensor of claim 7, wherein: the third magnetic tunneling junction andthe fourth magnetic tunneling junction have substantially similar ovalshapes each having a major axis substantially parallel to the secondeasy axis; and the first, second, third, and fourth magnetic tunnelingjunctions are substantially parallel to a base plane of the substrate.9. The magnetic sensor of claim 7, further comprising: a secondconductive wire passing through the third magnetic tunneling junctionand the fourth magnetic tunneling junction and carrying a current forsetting the third and fourth free magnetizations.
 10. The magneticsensor of claim 7, wherein: the third and fourth free magnetizationsrotate within respective planes of the third magnetic tunneling junctionand the fourth magnetic tunneling junction when an external magneticfield is applied to the magnetic sensor; and the conductivity of themagnetic sensor changes in response to the rotations of the third andfourth free magnetizations.
 11. The magnetic sensor of claim 10, whereinthe third and fourth free magnetization rotate in response to a secondexternal magnetic field or a second external magnetic field componentthat is substantially perpendicular to the second easy axis andsubstantially parallel to a base plane of the substrate.
 12. Themagnetic sensor of claim 1, wherein the first, second, third, and fourthmagnetic tunneling junctions are connected in parallel and the first,second, third, and fourth free magnetization rotate within respectiveplanes of the first, second, third, and fourth magnetic tunnelingjunctions in response to an external magnetic field, and theconductivity of the magnetic sensor changes in response to the externalmagnetic field component that is substantially perpendicular to the baseplane of the substrate.
 13. The magnetic sensor of claim 1, wherein thefirst inclined surface and the second inclined surface are symmetricallyformed on a dike structure or a groove structure on the substrate andform substantially same bevel angles with the base plane.
 14. Themagnetic sensor of claim 7, wherein: the substrate has a first inclinedsurface, a second inclined surface, and a base plane, the first inclinedsurface and the second inclined surface being symmetrically disposedwith respect to a medial axis of the base plane, and the first inclinedsurface and the second inclined surface forming substantially same bevelangles with the base plane; and the magnetic sensor further comprises: afifth electrode and a sixth electrode disposed on the first inclinedsurface; a seventh electrode and an eighth electrode disposed on thesecond inclined surface; a fifth magnetic tunneling junction and a sixthmagnetic tunneling junction disposed on the first inclined surfacebetween the fifth electrode and the sixth electrode and connected inparallel between the fifth electrode and the sixth electrode; the fifthmagnetic tunneling junction and the six magnetic tunneling junctionbeing arranged along a third easy axis; the fifth magnetic tunnelingjunction including a fifth free layer having a fifth free magnetizationand a fifth pinned layer having a fifth pinned magnetization; the sixthmagnetic tunneling junction including a sixth free layer having a sixthfree magnetization and a sixth pinned layer having a sixth pinnedmagnetization; the fifth and sixth pinned magnetizations each forming anangle of about 45 or 135 degrees with the third easy axis; and the fifthand sixth free magnetizations being parallel to the third easy axis andin substantially opposite directions; and a seventh magnetic tunnelingjunction and an eighth magnetic tunneling junction disposed on thesecond inclined surface between the seventh electrode and the eighthelectrode and connected in parallel between the seventh electrode andthe eighth electrode; the seventh magnetic tunneling junction and theeighth magnetic tunneling junction being arranged along a fourth easyaxis; the seventh magnetic tunneling junction including a seventh freelayer having a seventh free magnetization and a seventh pinned layerhaving a seventh pinned magnetization; the eighth magnetic tunnelingjunction including an eighth free layer having an eighth freemagnetization and an eighth pinned layer having an eighth pinnedmagnetization; the seventh and eighth pinned magnetizations each formingan angle of about 45 or 135 degrees with the fourth easy axis; and theseventh and eighth free magnetizations being parallel to the fourth easyaxis and in substantially opposite directions; the third easy axis andthe fourth easy axis being substantially parallel to the medial axis ofthe base plane; and the medial axis forming respective angles of about45 or 135 degrees with the first easy axis and the second easy axis. 15.The magnetic sensor of claim 14, wherein: the first and second magnetictunneling junctions are configured to sense a first magnetic fieldcomponent that is perpendicular to the first easy axis and parallel tothe base plane of the substrate; the third and fourth magnetic tunnelingjunctions are configured to sense a second magnetic field component thatis perpendicular to the second easy axis and parallel to the base planeof the substrate; and the fifth, sixth, seventh, and eighth magnetictunneling junctions are connected in parallel and configured to sense athird magnetic field component that is substantially perpendicular tothe base plane of the substrate.
 16. The magnetic sensor of claim 14,wherein the angles formed by the first, second, third, fourth, fifth,sixth, seventh, and eighth pinned magnetizations and the respectivefirst, second, third, fourth, fifth, sixth, seventh, and eighth freemagnetizations vary by −15% to 15%.
 17. A method for forming a magneticsensor, comprising: disposing a first magnetic tunneling junction and asecond magnetic tunneling junction between a first electrode and asecond electrode on a substrate, the first magnetic tunneling junctionand the second magnetic tunneling junction being aligned along a firsteasy axis, the first magnetic tunneling junction including a firstpinned layer, a first tunneling layer, and a first free layer, and thesecond magnetic tunneling junction including a second pinned layer, asecond tunneling layer, and a second free layer; connecting the firstmagnetic tunneling junction and the second magnetic tunneling junctionin parallel between the first electrode and the second electrode;setting a first pinned magnetization in the first pinned layer of thefirst magnetic tunneling junction and a second pinned magnetization inthe second pinned layer of the second magnetic tunneling junction alonga first pinned direction by subjecting the magnetic sensor to one ormore external magnetic fields during an annealing process, the first andsecond pinned magnetizations each forming an angle of about 45 or 135degrees with the first easy axis; and applying ampere fields to thefirst free magnetization in the first free layer of the first magnetictunneling junction and the second free magnetization in the second freelayer of the second magnetic tunneling junction by a setting current,the first and second free magnetizations being parallel to the firsteasy axis and in substantially opposite directions, wherein thesubstrate includes a first inclined surface, a second inclined surface,and a base plane, the first inclined surface and the second inclinedsurface being disposed symmetrically with respect to a medial axis ofthe base plane; and the first inclined surface and the second inclinedsurface forming substantially same bevel angles with the base plane; themethod further comprising: disposing the first magnetic tunnelingjunction and the second magnetic tunneling junction on the firstinclined surface between the first and second electrodes along the firsteasy axis; disposing a third magnetic tunneling junction and a fourthmagnetic tunneling junction on the second inclined surface between athird and fourth electrodes along a second easy axis, the third magnetictunneling junction including a third free layer, a third tunnelinglayer, and a third pinned layer, and the fourth magnetic tunnelingjunction including a fourth free layer, a fourth tunneling layer, and afourth pinned layer; connecting the first, second, third, and fourthmagnetic tunneling junctions in parallel; setting a third pinnedmagnetization in the third pinned layer of the third magnetic tunnelingjunction and a fourth pinned magnetization in the fourth pinned layer ofthe fourth magnetic tunneling junction along a second pinned directionby subjecting the magnetic sensor to the one or more external magneticfields during the annealing process, the third and fourth pinnedmagnetizations each forming an angle of about 45 degrees or 135 degreeswith a second easy axis on the second inclined surface; and setting athird free magnetization in the third free layer of the third magnetictunneling junction and a fourth free magnetization in the fourth freelayer of the fourth magnetic tunneling junction, the third and fourthfree magnetizations being parallel to the second easy axis and insubstantially opposite directions; and the first easy axis and thesecond easy axis are parallel to the medial axis of the base plane. 18.The method of claim 17, further comprising: disposing a third magnetictunneling junction and a fourth magnetic tunneling junction between athird electrode and a fourth electrode on the substrate, the thirdmagnetic tunneling junction and the fourth magnetic tunneling junctionbeing aligned along a second easy axis substantially perpendicular tothe first easy axis, the third magnetic tunneling junction including athird pinned layer, a third tunneling layer, and a third free layer, andthe fourth magnetic tunneling junction including a fourth pinned layer,a fourth tunneling layer, and a fourth free layer; connecting the thirdmagnetic tunneling junction and the fourth magnetic tunneling junctionin parallel between the third and fourth electrodes; setting a thirdpinned magnetization in the third pinned layer of the third magnetictunneling junction and a fourth pinned magnetization in the fourthpinned layer of the fourth magnetic tunneling junction along a secondpinned direction by subjecting the magnetic sensor to the one or moreexternal magnetic fields during the annealing process, the third andfourth pinned magnetizations each forming an angle of about 45 or 135degrees with the second easy axis; and applying ampere fields to thethird free magnetization in the third free layer of the third magnetictunneling junction and the fourth free magnetization in the fourth freelayer of the fourth magnetic tunneling junction by the setting current,the third and fourth free magnetizations being parallel to the secondeasy axis and in substantially opposite directions.
 19. The method ofclaim 18, wherein a projection of the one or more external magneticfields on a base plane of the substrate forms an angle of about 45 or135 degrees with at least one of the first easy axis or the second easyaxis.
 20. The method of claim 17, further comprising: setting the first,second, third, and fourth pinned magnetizations by positioning themagnetic sensor with respect to the one or more external magneticfields.
 21. The method of claim 17, further comprising: generating anexternal magnetic field for setting the first, second, third, and fourthpinned magnetizations, a first projection of the external magnetic fieldon the first inclined surface being substantially parallel to the firstpinned direction, and a second projection of the external magnetic fieldon the second inclined surface being substantially parallel to thesecond pinned direction.
 22. The method of claim 17, further comprising:generating a first external magnetic field parallel to the medial axisof the base plane of the substrate; and generating a second externalmagnetic field perpendicular to the base plane of the substrate; andsetting the first, second, third, and fourth pinned magnetizationssubstantially simultaneously by the first external magnetic field andthe second external magnetic field; and wherein a first projection of asummary of the first and second external magnetic fields on the firstinclined surface is substantially parallel to the first pinneddirection, and a second projection of the summary of the first andsecond external magnetic fields on the second inclined surface issubstantially parallel to the second pinned direction.